The invention relates to the field of televisions, for example those televisions having a wide display format ratio screen, which must interpolate video data to implement various display formats. Most televisions today have a format display ratio, horizontal width to vertical height, of 4:3. A wide format display ratio corresponds more closely to the display format ratio of movies, for example 16:9. The invention is applicable to both direct view televisions and projection television.
Televisions having a format display ratio of 4:3, often referred to as 4.times.3, are limited in the ways that single and multiple video signal sources can be displayed. Television signal transmissions of commercial broadcasters, except for experimental material, are broadcast with a 4.times.3 format display ratio. Many viewers find the 4.times.3 display format less pleasing than the wider format display ratio associated with the movies. Televisions with a wide format display ratio provide not only a more pleasing display, but are capable of displaying wide display format signal sources in a corresponding wide display format. Movies "look" like movies, not cropped or distorted versions thereof. The video source need not be cropped, either when converted from film to video, for example with a telecine device, or by processors in the television.
Televisions with a wide display format ratio are also suited to a wide variety of displays for both conventional and wide display format signals, as well as combinations thereof in multiple picture displays. However, the use of a wide display ratio screen entails numerous problems. Changing the display format ratios of multiple signal sources, developing consistent timing signals from asynchronous but simultaneously displayed sources, switching between multiple sources to generate multiple picture displays, and providing high resolution pictures from compressed data signals are general categories of such problems. Such problems are solved in a wide screen television according to this invention. A wide screen television according to various inventive arrangements is capable of providing high resolution, single and multiple picture displays, from single and multiple sources having similar or different format ratios, and with selectable display format ratios.
Televisions with a wide display format ratio can be implemented in television systems displaying video signals both at basic or standard horizontal scanning rates and multiples thereof, as well as by both interlaced and on interlaced scanning. Standard NTSC video signals, for example, are displayed by interlacing the successive fields of each video frame, each field being generated by a raster scanning operation at a basic or standard horizontal scanning rate of approximately 15,734 Hz. The basic scanning rate for video signals is variously referred to as f.sub.H, 1f.sub.H, and 1H. The actual frequency of a 1f.sub.H signal will vary according to different video standards. In accordance with efforts to improve the picture quality of television apparatus, systems have been developed for displaying video signals progressively, in a noninterlaced fashion. Progressive scanning requires that each displayed frame must be scanned in the same time period allotted for scanning one of the two fields of the interlaced format. Flicker free AA-BB displays require that each field be scanned twice, consecutively. In each case, the horizontal scanning frequency must be twice that of the standard horizontal frequency. The scanning rate for such progressively scanned or flicker free displays is variously referred to as 2f.sub.H and 2H. A 2f.sub.H scanning frequency according to standards in the United States, for example, is approximately 31,468 Hz.
Picture in picture processing is a feature wherein two television signals are simultaneously displayed on one display. The main or large picture fills most of the screen while the auxiliary or small picture is overlaid onto the large picture or next to the large picture. Where both signal sources and the display have the same format display ratio, for example 4.times.3, the small picture can be reduced in size by the same integer scale factor horizontally and vertically.
If the small picture has a format display ratio different than the display format ratio of the large picture and the display, then overlaying the small picture onto the display requires that the small picture be compressed differently in the horizontal direction than in the vertical direction. This is the case, for example, when attempting to display a 4.times.3 small picture signal source on a 16.times.9 display. If the 4.times.3 source were overlaid onto the large picture in the same manner on a 16.times.99 display as it is on the 4.times.3 display, that is, with equal size reduction in both the horizontal and vertical directions, the resulting small picture size and objects inside the small picture would appear 33% wider than normal. In other words, the image aspect ratio of the small picture would be distorted by 33%.